1. Field of the Invention
The present invention relates to a servo writer and a servo writing process, and particularly to a servo writer and a servo writing process, which can magnetize a servo band of a magnetic tape depending upon the degree of the thickness of a magnetic layer, disclosure of which is based on Japanese Patent Application Number 2003-296343, filed on Aug. 20, 2003, which is incorporated herein by reference.
2. Description of Related Arts
In recent years, a magnetic recording medium has increasingly be able to recorded at higher density, for example, there exists a recording medium for backing up data for computer has a capacity as high as 100 Gigabytes. For this reason, several hundreds of data tracks are formed in a width direction in the magnetic tape. In this connect, the width of the data track becomes very narrow accordingly, and a space between neighboring data tracks also becomes very narrow. For this reason, a technique has been suggested in U.S. Pat. No. 5,689,384 where in order to trace the recording/reading element of the magnetic head on the data track, a servo signal has been written on a magnetic tape in advance, the position of a magnetic head (the position of the magnetic tape in the width direction) is servo-controlled, while reading the servo signal by the magnetic heat.
The servo signal as described above has hitherto been written on a servo band on a non-magnetized magnetic tape by applying a recording current to the magnetic head of the servo writer so as to be magnetized in one direction. Specifically, as shown in FIG. 7A, in order to record a servo band SS on the non-magnetized servo band SB, a recording pulse current PC comprising a zero current and a plus pulse current has hitherto been run. When such recording pulse current PC is used, the magnetic tape MT is not magnetized only within the region of servo pattern SP in the case of the zero current of the recording pulse current PC, and if the plus pulse current is run, the servo pattern SP is magnetized in one direction through a leaked magnetic flux from a servo gap of the magnetic head. As a result, the servo signal SS is written. Data band DB on which data signal is written is between the servo bands SB and SB.
The servo signal SS is composed so that one servo pattern SP is formed by burst Ba, which is a magnetized portion in a state of two stripes each having positive inclination angle relative to the driving direction (transferring direction), and the following burst Bb, which is a magnetized portion in a state of two stripes each having negative inclination angle relative to the driving direction, and such servo patterns SP are repeatedly formed in the lengthwise direction at prescribed intervals. In this prior art, while the servo pattern SP is composed of two stripes each positively and negatively inclining in this case, the construction of the servo pattern SP may be suitably modified. For example, it may be composed of five stripes each positively and negatively inclining, or five stripes each positively and negatively inclining and four stripes each positively and negatively inclining may be alternatively formed. For better understanding, the servo pattern SP is shown exaggeratedly relative to the magnetic tape MT in FIG. 7A.
On the other hand, in the device for recording/playing a magnetic tape the change in the magnetic field of the servo signal SS is detected by the change in the electric resistance through the servo signal reading element (MR element), and is outputted as a differential waveform (voltage value) as the reading signal. For this reason, as the change in the electric resistance of the MR element becomes large, the peak voltage value of the reading signal of the servo signal SS becomes large, enhancing an S/N ratio of the reading signal. Consequently, in the case where the change in the servo signal SS itself is large or in the case where the region to be read is large due to wide width of the servo signal reading element (MR element), the peak voltage value of the reading signal RSL of the servo signal becomes large as shown in FIG. 7C.
In the magnetic recording medium, it is expected that the recording capacity per one cartridge becomes much higher dense up to several terabytes. Consequently, the number of the data tracks in the magnetic tape is increased, the space between the neighboring data tracks becomes much more narrower, and the thickness of the magnetic tape becomes thinner. This decreases the magnetic amount, which can be detected at the time of reading the servo signal, and reduces the change in the magnetic amount of the servo signal SS, which can be detected by the servo signal reading element. Consequently, as shown in FIG. 7D, the peak voltage value of the reading signal RSS of the servo signal Ss becomes small, and the S/N ratio of the reading signal RSS is deteriorated. As a result, the recording/playing device of the magnetic tape cannot read the servo signal SS in a precise manner, and highly precise control of the position cannot be performed.
An object of the present invention is to provide a servo-writing process, which can magnetize a servo band of a magnetic tape depending upon the degree of the thickness of a magnetic layer.